#include <fstream>
#include <algorithm>
#include <vector>
#include <queue>
#include <climits>
#include <stack>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

const int NMAX = 1000005;

vector < vector <int> > adjList;
vector < pair <int,int> > edges;

int dist[NMAX],viz[NMAX],sol[NMAX],cnt;

void euler(){
    stack <int> st;
    st.push(1);
    while(!st.empty()){
        int cand = st.top();
        if(!adjList[cand].empty()){
            int x = adjList[cand].back();
            adjList[cand].pop_back();
            if(!viz[x]){
                st.push({edges[x].first == cand ? edges[x].second : edges[x].first});
                viz[x] = 1;
            }
        }
        else
        {
            st.pop();
            sol[++cnt] = cand;
        }
    }
}
int main()
{
    int n,m;
    fin>>n>>m;
    adjList.resize(n + 1);
    edges.resize(m + 1);
    int x,y;
    for(int i = 1;i <= m;i++)
    {
        fin>>x>>y;
        adjList[x].push_back(i);
        adjList[y].push_back(i);
        viz[x]++;
        viz[y]++;
        edges[i] = {x,y};
    }
    for(int i = 1;i <= n;i++)
    {
        if(viz[i] % 2)
        {
            fout<<"-1";
            return 0;
        }
        viz[i] = 0;
    }
    euler();
    for(int i = 1;i <= cnt;i++)
        fout<<sol[i]<<" ";
    return 0;
}